1. Field of Invention
The present invention relates to a manufacturing method capable of preventing the corrosion and contamination of a MOS gate. More particularly, the present invention relates to a manufacturing method that uses a rapid thermal process to form a protective oxide layer over part of the MOS gate capable of preventing corrosion and contamination during subsequent etching operations.
2. Description of Related Art
Metal-oxide-semiconductor (MOS) transistor is an important semiconductor device in an integrated circuit. The MOS transistor acts like a switch that can be switched ON or OFF through its gate. Since the gate is a major component in the operation of the MOS device, any deviation in the gate's voltage sensitivity can lead to serious control problems.
FIGS. 1A through 1C are schematic, cross-sectional views showing the progression of manufacturing steps according to a conventional method of producing a MOS device. First, as shown in FIG. 1A, a gate oxide layer 12 is formed over a silicon substrate 10. Then, a polysilicon layer 13 is deposited over the gate oxide layer 12. Next, a barrier layer 14 is formed over the polysilicon layer 13. The barrier layer 14 can be used to prevent the cross-diffusion of different type ions inside the polysilicon layer 13. For example, in a dual gate MOS transistor, the P-type ions in the P-type gate and the N-type ions in the N-type gate can diffuse into each other. Thereafter, a silicide layer 15 and then a cap layer 16 are deposited in sequence over the barrier layer 14.
Next, as shown in FIG. 1B, photolithographic and etching operations are conducted to pattern a gate region. Subsequently, using the cap layer 16 as a mask, a first ion implantation is carried out, implanting ions into the substrate to form lightly doped source/drain regions 17.
Thereafter, as shown in FIG. 1C, spacers 18 are formed on the sidewalls of the gate. Finally, using the gate and the spacers 18 as masks, a second ion implantation is carried out implanting ions into the substrate again to form heavily doped source/drain regions 11.
In general, the barrier layer 14 is formed using titanium material such as titanium nitride. However, titanium nitride is vulnerable to acid attack in subsequent operation whenever the gate sidewall is exposed, thereby easily contaminating manufacturing stations. FIG. 2 is a cross-sectional view indicating the position of corrosion 19 on the sidewalls of a barrier layer in a MOS gate.
In light of the foregoing, there is a need to improve the method for manufacturing MOS gate.